HK 730 making noises...

[RockysDad]

I have a vintage Harmon Kardon 730 receiver that I am trouble with crackling noise out of the right output. Its not in the amp section because there is a jumper that can separate it from the preamp and testing the amp by itself is clean. The power supply seems to be okay since the power amp is fine. Therefore it must be the preamp. I think... Other clues are that its not volume or sourse dependent. Its just sort of there, sometimes worst them other times.

Just recently, with the power "off" the right speaker started to crackle and pop loudly for no apparent reason. I am trying to figure that one out. I mean the power was off and yet there was crackling and popping noises being outputed. Very strange. It seems that maybe a cap is being discharged somehow somewhere but the power amp has to be powered up doesn't it? So I am looking for ideas on where to start looking. I do have a schematic but am out of ideas on where to look. I did change all the biggger caps in the power supply section and all the caps in the pre-amp section. It still crackles some but not as bad.

Bad switch maybe, power supply for the pre-amp section? I wish I had a scope but don't. What else can I do?

TIA...

 

[amplifierguru]

Hi Rockysdad,

It's old so PS electro's are sus.

Do L and R channels of the preamp section share the same power supply? If not you could swap the C's to see if it changes L <->R.

Cheers,
Greg

 

[jblmar]

Could be an electrolytic cap in the PS or a bad diode. Some designs used diodes for a quick discharge.
Ron